Sampling small older populations:

Methods and challenges of a dementia prevalence study

NZSA2024

Claudia Rivera-Rodriguez, PhD

New Zealand changing population

Image 1

The need for a prevalence study

Image 1

Feasibility study (2020)

Image 1

  • Found that the sampling/doorknocking strategy was reasonable

  • We were able to train up multi-ethnic interviewers

  • Response rate at the door-knocking stage was 75% but at subsequent stages was about 25%

  • Demonstrated that a prevalence study was feasible in Māori, Chinese, Indian and Pākehā, but not in Pacific populations.

IDEA Study

  • AIM: Establish the true current prevalence of dementia in NZ
  • This study is for Chinese, Indian and Pākehā
  • There is separate study for Māori(running at the moment too)
  • This talk presents the sampling design and lessons learned from the IDEA study

Sampling strategy

Frame: Territorial autorities

Image 1

Sampling phases

Image

  • Phase 1: Stratified by TA and rurality & oversampling of Chinese/Indian(65+) dense areas

  • Phase 2: Proportion of meshblocks sampled from each area – depends on the density of Chinese and Indian.

Phase 3

Image

Sample sizes for each domain

  • We run lots of simulations to identify sensible sample parameters: Image

Sample sizes for each domain

We decided on a margin of error of about 0.03,

Phase 1: Areas

Cons

  • Meshblocks with only businesses, not residential dwellings: We will replace these with the closest meshblock (based on selection probability) from the same area.

  • Door-knocking is expensive and difficult.

  • Consent rates vary across ethnicities: We will need to adjust for this.

  • Data processing from questionnaires in four different languages.

Recruitment over time